A 21st century week

Three  international events took place this week: the AWTF, the EGOI and the IMO. I have chosen the AWTF to attend in person (problems, results, top 5 on the left, mirror results, analysis in Japanese, broadcast recording). 6 out of 12 finalists were born in the 20th century, and the highest place the veterans have achieved was place 4. It feels a bit surreal that Andrew and Kevin are the veterans now. The podium places all went to the new generation from China — congratulations on the amazing performance! With rare exceptions, it took the contestants around 2 hours to solve B, C or D, if they could solve one of those at all. Zhou Kangyang, however, collected 2 of those exceptions by solving B and C very fast, and was the only contestant to solve D, so he was in the league of his own on the day.

I want to highlight problem B from the round: you are given n<=100 days and m movies, the i-th movie running from day l_i to day r_i (all pairs (l_i, r_i) are different). Find the sum of the following values: for each of the 2^m sets of movies, what is the maximum amount of different movies from that set one can watch, if one only watches at most one movie per day?

The 5th EGOI took place in Germany (problems and analysis, results, top 5 on the left). The scores were very close starting from place 4, but the first three places were separated quite visibly, even if the differences meant solving just a few more subtasks. Congratulations to Paulina, Anastasiia and Clara on the great results!

Problem C from the first day likely allowed many different approaches, including solving it fully on paper or by writing some helper programs: there are n<=50 players playing bingo. Each player will have a card with exactly 12 numbers, each between 1 and 50. Then, all numbers from 1 to 50 will be read out in some order, and the first player whose all 12 numbers have been read out will be declared the winner. Can you design the contents of the players' cards in such a way that there will never be a tie? This is essentially an output-only problem since there are only 50 fully independent test cases (n=1, n=2, ..., n=50). How many of those can you get? Bonus points if you can meaningfully use a computer to make progress.

The IMO 2025 (problems, results, top 5 on the left) is not typically within the scope of this blog, but there were two independent crossover points this time that made me bring it up. First, the skills required to solve IMO problems and the competitive programming problems (especially the AtCoder flavor), although not the same, are quite related, and strong competitors can often do both and move from one area to the other. Second, both areas are now at the forefront of the AI race, as they provide both nice datasets and objective evaluation opportunities for the general reasoning and general problem solving skills. It is unexpected and cool how what used to be a fun hobby now has the world's attention. Congratulations to the IMO 2025 participants who still hold their own against the AI, and I hope to meet some of you at the competitive programming events one day :)

Finally, Codeforces held Order Capital Round 1 to wrap up the week (problems, results, top 5 on the left, analysis). tourist has shown that the 20th century folk still stand a chance, and regained his first place in the overall ratings as a result. Well done, and thanks!

Thanks for reading, and check back next week.

AWTF25 heuristic day

As discussed, one had to get assistance from AI to even watch today's AWTF25 heurstic broadcast: you can see an example live automatic translation on the left. It was enough to understand the broadcast in rough terms, but a lot of nuance was likely lost.

For those who missed it, there was not too much suspense in the human competition, as Psyho seemed to be head and shoulders above his competitors, but it was quite close (and possibly still is, since there were only 50 pretests?) between Psyho and OpenAI's automated solver (preliminary exhibition top 5 on the right). The final results will be revealed tomorrow evening Tokyo time together with the Algorithm competition results.

Speaking of which, tune in tomorrow to watch me and Riku commentate on the 5-hour Algorithm finals in English! You can also check out the finalists' presentation. While last year I was 14th on the qualification ranking and could have been a participant, this time I am squarely in the commentator realm. In case you have topic ideas that we could discuss during the 5 hours (while the contestants are stuck on A, as usual), please share in comments!

AWTF25 arrival day

AtCoder World Tour Finals 2025 (official website with the participant intros) takes place this week in Tokyo, and it is the fourth cphof-worthy event of the year already!

For the third year running, I was greeted by a weather alert on my arrival in Tokyo, this time for a typhoon like two years ago, and like two years ago the typhoon eventually missed Tokyo completely. It is of course better to be prepared even if nothing happens, than to be unprepared and be caught unaware, so no complaints here :)

Tomorrow (July 16) is the first ever Heuristic finals for AtCoder (announcement), and besides a few familiar faces from the past Marathon/Heuristic competitions it features a whole lot of new stars and an AI competitor to boot! There will be a stream in Japanese, which is not yet my strong side (but maybe that's the language of competitive programming of the future, given how important AtCoder and the community in Japan are for moving our entire field forward), but I still expect it to be exciting to watch, so tune in tomorrow!

EUC 2025

Once again the ICPC Quest brings this blog out of hibernation :) So, as the quest requires, greetings from Porto where the 2025 ICPC European Championship (EUC) takes place this Sunday!

The EUC is a new contest that was launched last year, so this is the second edition. It brings together the top teams from 4 European regionals, providing them both an additional qualification path to the ICPC World Finals (detailed rules), and a significant onsite competition of its own, giving many teams who will not make it to the World Finals an opportunity to meet other students and enjoy the atmosphere of a big international competition, while keeping the travel costs in check. I am very happy to support this competition by volunteering as a judge for the second time!

We are also running a mirror contest on Codeforces, so come try it in a few hours! I think the problems are quite nice.